Electromagnetic locks have enjoyed widespread usage in security applications, such as for securing a door against ingress and egress. Electromagnetic locks have proven to be reliable and versatile systems for security applications. Such locks typically allow instant ingress or egress during an emergency situation. Electromagnetic locks also readily provide a failsafe feature by unlocking in the event of a power failure.
Delayed unlocking systems have been integrated into electromagnetic locks to delay ingress or egress through a secured doorway. Electromagnetic locks employing delayed unlocking have found particular use in hospitals and nursing homes. The delayed unlocking of a secured door allows for security personnel or hospital staff to determine whether the ingress or egress is appropriate for a particular patient. Therefore, in non-emergency situations, hospitals or nursing home personnel can restrain a patient from exiting from the facility unattended.
An example of an electromagnetic lock having a delay feature is disclosed in Logan U.S. Pat. No. 4,720,128. The housing for the electromagnet is mounted to a door frame. A switch is located adjacent to the electromagnet. An armature opposite the electromagnet and a block opposite the switch are mounted to the door associated with the door frame. Actuation of the switch by the block begins a delayed egress sequence. The housing is of relatively large size due to the electromagnetic lock and the adjacent switch associated with the electromagnet. Furthermore, the switch may be exposed to tampering.
Bailey U.S. Pat. No. 4,915,431 discloses an electromagnetic lock system with a switch assembly which provides a door-movement alert for delayed egress or a security alert. This electromagnetic lock employs an armature which is floatably attached to the door by a plunger-bolt assembly fixed to the door. An electromagnet is fixed to the door frame. A door-movement alert switch comprises a pushbutton switch supported on the electromagnet and a plunger supported on the plunger-bolt assembly. A spring force-biases the plunger into mating contact with the switch when the door is electromagnetically locked to establish a first switch-actuation state. The force-biased spring maintains the switch in the first state while the armature is magnetically restrained. When the door is opened and the door-movement distance is slightly less than the armature float distance, the plunger is partially drawn into a plunger housing fixed on the plunger-bolt assembly. In this electromagnetic lock assembly, the armature is essentially not biased toward the door by a spring acting between a mounting bolt and the armature, and the switch assembly is relatively complex.
Another example of an electromagnetic lock system employing delayed unlocking is disclosed in Frolov et al U.S. Pat. No. 5,065,136, which is assigned to the assignee of the present invention. An electromagnet is mounted to a lock frame to provide a rocking movement. The lock frame is fixed to the door frame. Motion of the door while the electromagnet is electromagnetically bonded to the associated armature correspondingly pivots or rocks the entire electromagnet within the lock frame. This rocking motion actuates a switch. The switch actuation activates an alarm, begins a delay sequence for unlocking or otherwise initiates various security-related functions.